We can expect cyclist speeds and stage times nearly identical to last year’s event, which featured 20 stages plus a prologue time trial, over 3,497km.

The time taken to complete individual stages ranged from 51 minutes and 24 seconds (stage nine: a flat time trial over 38km, with a mean speed of 48.4 kilometres per hour) to five hours, 42 minutes and 46 seconds (stage 12: a medium mountain-stage over 226km, with a mean speed of 39.5km/h) with an overall mean race-pace of 39.9km/h.

Given such speed and consistency of pace, it probably seems obvious that hydration and nutrition are crucial.

Drink up

Hydration is the first priority for competitors in any prolonged endurance event. Sweat rates vary between individuals and depend greatly on the workload (heat produced by muscle contraction) and climatic conditions (temperature, humidity, air passage over the body) but are probably about one-to-two litres an hour for most Tour cyclists.

Australian rider Simon Gerrans, in the yellow jersey after his team won stage four of this year’s Tour. Yoan Valat/EPA

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Excessive fluid loss can lead to a loss of power, so it’s recommended that any athlete engaged in vigorous exercise minimises fluid losses to no more than 2-3% of body mass during exercise;electrolytes (such as sodium and potassium) are also lost in the sweat and should be replaced if sweating is heavy and exercise prolonged. But here’s where things get a bit tricky.

In a sport where a 1% change in performance could be the difference between wearing the coveted yellow jersey and second place, fluid over-replenishment may also equate to carrying unnecessary weight. A 70kg rider who has lost two litres of sweat (about 3% of body mass) has less mass to push uphill.

So that rider’s performance should be better on climbs, as long as his power output is not compromised by the mild dehydration. Only with long hours of testing can a Tour rider determine their own optimal balance between hydration, body-mass and power output.

Eat up

Consuming a sufficient amount of dietary carbohydrates before, during and after exercise is also crucial. We store carbohydrates predominantly as muscle and liver glycogen, and a tiny amount as blood glucose. These are the key fuels for muscle contraction during intense exercise: glycogen depletion below a critical threshold will result in a dramatic decline in performance (known in cycling as “bonking” or “hitting the wall”).

Although sports drinks are one practical way of delivering fluid, electrolytes and carbohydrates (simple sugars such as glucose and fructose, and complex carbohydrates such as maltodextrin), a rider could do similar with water, jam sandwiches and a banana.

Balancing act

To support optimum performance over the three-week Tour, riders also need to consume enough daily energy to offset their high expenditures, and adequate dietary protein to support muscle recovery.

Negative energy balance (such as when the total daily energy from food and drink is less than that expended) or inadequate dietary protein can lead to metabolic changes and cannibalism of existing body proteins to produce additional energy for cells.

It sounds worse than it is, but those changes may impair exercise performance. Tour riders attempt to minimise the risk of impairment by consuming as many kilojoules (kJ) of energy as they expend.

Which raises the obvious next question: how much energy does a Tour de France riders actually expend, and what do they eat and drink?

In the pros’ pockets?

Well before the advent of sports nutrition, riders competing in early Tour editions were pretty much left to their own devices to complete each stage, which included foraging for themselves along the way to satisfy their hunger and thirst.

The first Tour, and not a PowerBar to be seen.Wikimedia Commons

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Times have changed although, surprisingly, there is very little published data on the dietary practices of modern-era Tour de France riders.

That’s around two and half times more energy than a typical sedentary male of similar size might expend. Fluid intake averaged 6.7 litres a day (the largest daily intake was 11.8 litres!) with 61% consumed during cycling.

Dietary carbohydrates accounted for about 61% of their energy intake, fats about 23% and proteins about 15% (nearly 230 grams a day for a 70kg rider).

Half of their daily energy was consumed during exercise, mostly as carbohydrate (about 94 grams an hour), and sports drinks alone contributed 15% of their total daily energy. Interestingly, sweet cakes eaten during rides were the major energy provider in the diets.

High in simple sugars and fats, these were energy dense and clearly palatable for the riders. The rice cake recipe, below, offers a more savoury alternative:

Will winning or finishing second in the 100th Tour hinge on a well-timed drink or bite to eat? We’ll never know, but we do know that the sports nutrition behind the scenes of professional cycling has moved a long way from foraging for food and water in the French countryside.

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